1. Field of the Invention
The present invention generally relates to a bypass type prefilled syringe in which a bypass for establishing communication between front and rear compartments for preliminarily storing two components, for example, powdery medicament and pharmaceutical liquid, respectively is formed on a tubular body, and more particularly to a gasket for dividing interior space of the tubular body of the bypass type prefilled syringe into the front and rear compartments.
2. Description of the Prior Art
FIGS. 6 and 7 show a sealing state and a communication state between a front compartment 6 and a rear compartment 7 of an elongated hollow tubular body 1 of a conventional bypass type prefilled syringe, respectively. A front assembly 15 includes an injection needle 10 and a cap 11 for covering the injection needle 10 so as to protect the injection needle 10 and is mounted on an outer periphery of a front end portion of the tubular body 1. In FIG. 6, the conventional bypass type prefilled syringe includes a first sealing member 3 which is mounted in the front end portion of the tubular body 1, a second sealing member 4 which is attached to a front end of a plunger rod 2 and is disposed at a rear end portion of the tubular body 1 and a gasket 5 which is slidably inserted between the first and second sealing members 3 and 4 in the tubular body 1 and divides interior space of the tubular body 1 into the front and rear compartments 6 and 7. Powdery medicament P and pharmaceutical liquid L are preliminarily, respectively, stored in the front and rear compartments 6 and 7 so as to interpose the gasket 5 therebetween.
A bypass 1a is formed by bulging a peripheral wall of the front compartment 6 of the tubular body 1 radially outwardly. On the other hand, a finger grip 12 is mounted on an outer periphery of the rear end portion of the tubular body 1. By forwardly depressing the plunger rod 2 in the direction of the arrow a in FIG. 7 from the state of FIG. 6 to the state of FIG. 7, the gasket 5 is advanced by the second sealing member 4 by way of the pharmaceutical liquid L so as to be disposed between a front end portion and a rear end portion of the bypass 1a. At this time, a gap for directly linking the front and rear compartments 6 and 7 is defined between the gasket 5 and the bypass 1a, so that the front and rear compartments 6 and 7 are communicated with each other by the bypass 1a and thus, the pharmaceutical liquid L is introduced from the rear compartment 7 into the powdery medicament P in the front compartment 6 along a flow path indicated by the arrow b in FIG. 7. Then, when the powdery medicament P is sufficiently dissolved or dispersed in the pharmaceutical liquid L by shaking the tubular body 1, injection liquid is formed.
At the time of communication between the front and rear compartments 6 and 7 through the bypass 1a in this conventional bypass type prefilled syringe, the pharmaceutical liquid L is fed under pressure into the front compartment 6 in a state where the injection needle 10 is mounted on the tubular body 1. At this time, the gasket 5 is disposed between the front end portion and the rear end portion of the bypass 1a and the gap for directly linking the front and rear compartments 6 and 7 is defined between the gasket 5 and the bypass 1a as described above. Thus, in case a user forcibly depresses the plunger rod 2 from the state of FIG. 6 to the state of FIG. 7, a so-called squirt phenomenon in which the pharmaceutical liquid L spouts from the bypass 1a vigorously may happen, thereby resulting in such an inconvenience that the pharmaceutical liquid L impinges on the first sealing member 3 and then, leaks out of the injection needle 10.
Meanwhile, FIG. 8 shows a sealing state between the front and rear compartments 6 and 7 of the tubular body 1 of a known bypass type prefilled syringe disclosed in U.S. Pat. No. 4,599,082. In this known bypass type prefilled syringe, a gasket 20 is employed. As shown in FIG. 9, the gasket 20 has a front end face 20a and a rear end face 20b and includes ribs 24, 26 and 27. Meanwhile, an annular recess 25 is provided between the ribs 24 and 26 and a plurality of grooves 28 extending obliquely relative to an axis of the gasket 20 are formed on the rib 24 so as to open to the front end face 20a. In order to improve agitation and mixing of the pharmaceutical liquid L and the powdery medicament P at the time of communication between the front and rear compartments 6 and 7 via the bypass 1a, the pharmaceutical liquid L is introduced from the grooves 28 into the powdery medicament P obliquely relative to the axis of the gasket 20.
However, in contrast with the conventional construction shown in FIGS. 6 and 7 in which the injection needle 10 is mounted on the front end portion of the tubular body 1, this known bypass type prefilled syringe has a construction in which a distal end cap 35 is mounted on a distal end 34 of the tubular body 1. Thus, as described at column 8, lines 3 to 9 of the above mentioned U.S. Patent, mixing operation of the pharmaceutical liquid L and the powdery medicament P is performed by depressing a plunger rod in a state where the distal end 34 of the tubular body 1 is directed upwardly after the distal end cap 35 has been removed from the distal end 34 of the tubular body 1. Therefore, the gasket 20 merely serves to improve agitation and mixing of the pharmaceutical liquid L and the powdery medicament P and thus does not serve to prevent leakage of the pharmaceutical liquid L from an injection needle due to the squirt phenomenon.
Accordingly, an essential object of the present invention is to provide, with a view to eliminating the above mentioned drawbacks of prior art, a gasket for a bypass type prefilled syringe which prevents a squirt phenomenon of pharmaceutical liquid at the time of communication between front and rear compartments of a tubular body by way of a bypass such that powdery medicament can be sufficiently dissolved or dispersed in the pharmaceutical liquid.
In order to accomplish this object of the present invention, a gasket for a bypass type prefilled syringe having a tubular body formed with a bypass for establishing communication between front and rear compartments for preliminarily storing medicament and pharmaceutical liquid, respectively, according to the present invention divides interior space of the tubular body into the front and rear compartments and includes a plurality of circumferential ribs which include at least first, second and third circumferential ribs disposed sequentially further away from the front compartment. A plurality of annular recesses are each formed between neighboring ones of the circumferential ribs and include at least a first annular recess formed between the first and second circumferential ribs and a second annular recess formed between the second and third circumferential ribs. A first axial slot extends through the first circumferential rib and the first annular recess, while a second axial slot is formed at a circumferential position of the second circumferential rib deviating from the first axial slot so as to bring the first and second annular recesses into communication with each other. At the time of communication between the front and rear compartments via the bypass, a bent outflow path for delivering the pharmaceutical liquid into the front compartment in a state where the tubular body at a front end side of the bypass is closed by a front end portion of the gasket is sequentially formed by the second annular recess, the second axial slot, the first annular recess and the first axial slot.